Acetylcholinesterase inhibiting pesticides (i.e., organophosphate (OP) and carbamate pesticides) are widely used in the US and worldwide. Long-term neurological and neurobehavioral health effects of exposure to these pesticides are not well characterized. The investigators propose an epidemiological investigation of associations between long-term organophosphate and carbamate pesticide exposure and neurological and neurobehavioral health outcomes among approximately 700 pesticide applicators in Iowa and North Carolina (350 per state). Study participants will be recruited from among pesticide applicators currently enrolled in the Agricultural Health Study (AHS), a federally funded cohort study of licensed pesticide applicators from Iowa and North Carolina. Detailed information about individual exposure to a wide range of pesticides is available from the AHS. Applicators have been observed to experience wide variation in cumulative pesticide exposure making them suitable for investigation of health effects. Neurological and neurobehavioral health outcomes will be assessed with a battery of validated neurobehavioral tests that have been used successfully in previous investigations of neurotoxicant exposed individuals. The Primary Aim of the proposed investigation is to examine associations between cumulative lifetime exposure to the sum of all OP and carbamate pesticides and performance on selected measures of peripheral and central neurological function while controlling for effects of known covariates. A Secondary Aim of the proposal is to examine the effect of polymorphisms of paraoxonase, cytochromes P450, and glutathione-S-transferases (potential genetic modifiers of OP pesticide effect) on the association between exposure to OP pesticides and neurological and neuropsychological measures.